Multiple diaphragm



Se t 14 1926. 1,599,735

M. E. YVOLVEKAMP 1 IULT I PLE DIAPHRAGM Filed July 3. 1924 1 l/VVE/VTOR.

Patented Sept. 14, 1926.

UNITED STATES PATENT OFFICE.

MARI E. WQLY'EKAMP, OAKLAND, CALIFORNIA.

MULTIPLE DIAPHRAGM.

Application filed July 3, 1924. Serial No. 724,164.

My invention relates to multiple diaphragms for phonographs, recorders, telephones, loud speakers, and other sound producin instruments.

It as for its object the combination of two or more diaphragms of different thicknesses, or of different areas of vibration, or of different materials, in such manner that their different fundamental vibrations combine to produce a more agreeable tone than that of the fundamental which is heard when one diaphragm is used.

ring of 2 centimeters radius that clamps the dia hragms in the reproducer.

*igures 5, 6, and 7 are sectional views of three phonograph dia-phragms of the same thickness but of different radii being respectively I p 1/ 1/ and 1 centimeter.

Figure 8 is a sectional view of a multiple diaphragm as mounted for the reproducer, consisting in three diaphragms of single, triple, and double thickness.

Figure 9 is a sectional view of a repreducer comprising the same multiple diaphragm as shown in Figure 8.

Figure 10 is a sectional view of a multiple diaphragm for a radiophone receiver, consistlng in two diaphragms of double and sin le thickness.

igure 11 is a side elevation of a radiophone receiver, except the ebonite cap and the multiple diaphragm which is shown in sectional views, the multiple diaphragmbein the same asshown in Figure 10.

Tf a loud voice sings in a phonograph, one hears distinctly a more or less continuous disagreeable tone remaining of the same high itch and which comprises principally the undamental note of the reproducer-diaphragm, that is the gravest natural note when the diaphragm vibrates to and fro as a whole.

Such a continuous high .note, as produced by the phonograph, and also by the common telephone receiver, and even more distinct by the loud speaker, is more unpleasant to the car than acomposite tone comprising notes which are in harmony with each other.

The eight notes of the. natural or diatonic scale are expressed by the rates of vibration The most perfect consonance for two notes is when they form an octave, that is, when their vibrations per second are in the ratio 1 2; next comes the fifth 213-; after that the fourth 3 z 4; then the major third 4: 5. The smaller the two numbers which express the ratio of the two different rates of vibration, the more perfect is the consonance of the two sounds. I

The frequency n of the fundamental note of a thin circular plate of isotropic material, clamped at the edge, may be calculated when is known Youngs modulus of elasticity E, the density d, the thickness or height h, and the radius 'r', by means of the simplified general formula h E !t 4812F/E1 in which E is expressed in kilogrammes per square millimeter, and h and r in centimeters. Poissons ratio of lateral contraction to longitudinal elongation, has been eliminated in Rayleighis formula by taking d 7.7 p c which gives for the iron telephone dia phragms For a diaphragm, thick 0.017 centimeter and with a radius of 2 centimeters, the fundamental note will be of 10 12 vibrations per second.

For aluminium, we may take J'ass which gives for alui'ninium diaphragms 71, n=2ll500 For an aluminium diaphragm, thick 0.03 centimeter and with av radius of 2 centi meters, the fundamental note will be of 2113 vibrations per second.

The multiple diaphragins, used in my experiments in the reproducer of Figure 9, were of mica, iron, aluminium, wood, and celluloid. The mica, aluminium, wood, and celluloid diaphragms were cut from one sheet of material, respectively thick 0.007, 0.035, 0.00, and 0.033 centimeter. The iron diaphragms were cut from radio-receiver diaphragms of a well-known brand and were thick 0.017 centimeter after their coat of japan-lacquer had been removed. From these were made the diaphragms of double and triple thickness of Figures 2 and 3, by fastening their surfaces together by means of a little glue, or, as in the case of iron, by means of a little solder, which was conveniently applied in paste form.

The diameters of these diaphragms, as represented by Figures 1, 2, and 3, were centimeter, but the diameter of the clamping steel ring of Figure l was at centimeters and hence were the radii of their areas of vibration 2 centimeters.

The clamping steel ring of Figure at, the same as shown by l in Figure 9, is open for passage of the stylus arm A.

The edges of the three diaphragms 1, E, and 2 in Figures 8 and 9, of single. tripple, and double thickness, are separated from each other by rubber washers 5, and at their centers by little pieces of rubber tubing 6, around the stem of the long screw 7, which is threaded into the collar-nut S at the end of the stylus arm A, and with the head of the screw resting on this collar-nut. Lit the other side of the screw is a collar-nut 10. provided with a little arm 11 to facilitate its being turned by the finger in order to screw the three diaphragms fast between the two collar-nuts.

All different combinations of two diaphragms of the same material but of different thicknesses were tried out, listening to the relative tonal strength as well as to the timbre of the whistling sound that accompanied a loud voice. \Vith one diaphragm this note is strong, more or less continuous, and poor in quality, and a similar note is heard of the same strength when two dia- ",hragms of the same thickness are used. The other combinations, triple thickness outside plus double thickness inside, 3+1, 2+3, 2+1, 1+3, and 1+2, gave all tones of bet ter (piality, and, what also important, the relative strength of the false tone was in all cases distinctly less.

The best timbre and least relative strength of the false tone was obtained by the combir-=ion oi two diaphragms of double and e thickness, 2+1, or 1+2, forming to- Xext came the lii'th 3+2, or 2+3, whereas 1+3, the whistling sound was more ied, especially direct from the repro- These results were in general the 5 ee for re multiple diaphragms made of mica, iron, alunnminn, wood, or celluloid.

The re on why the relative strength of tone is l niiarked is probably due act that the fuinlan'iental of one rm a free viln'ation, whereas in bination of two diaphragms they iGl'CQ their different fundamental vi- .ons on one another.

The thi diaphragms gave in some srunei t less total. volume of sound, g tralitmadelittle diil'erence which diaphragm in a combination was placed outside and which inside.

ia znilar experiments were made with mica, iron, and alnn'rinium diaphragms of different radii, as shown in Figures G, and '7. These diaphragms were clamped at their edges between flat metal rings, which. were soldered together, or, in the ase of mica,

3 iply glued. together.

the radii from the centers to the metal rings were respectively w 1' 1 these .lnee oiaplii gins am. the diaparagms "nne material of single and double which were of 20 nnllnneters For convenience, I will denote them by their radi in n'iilliineters, and, when double thickness is meant. by the prefix double. The best timbre and least relative intensity of the false tone were obtained in 20+1l and l.i;+l0. both forming an octave. The combination 20+l-1 gave a larger total volume ()1 sound, and in general, the diaphragms of .ess size gave less total volume of sound. The double 20 could take the place of the bit gave a larger volume of sound. Next n relative strength and timbre of the false one came the fifth, 1T+1l. and 1T+double 0, then the fourth, 20+l7, and next the double octave, 90-440, whereas double 20+14 gave the some or a similar strong disagreeable whistle as one diaphragm or the combination of two diaphragms of the same thickness and radius.

If three equal diaphragms 20+20+20 are used, they again give thatstrong disagreeable whistle, and this was the case for all five different kinds of material.

All 6 different positions in the combination of the three diaphragms of Figures 1, 2, and 3, were tried out with mica, iron, and aluminium, and the results were all distinctly superior to those obtained with two diaphragms, as well in timbre as in less tonal strength of the false tone.

The combination 2+3+1 is shown in Figures 8 and 9.

They form the combination of an octave, a fifth, and a fifth of the octave.

In the chime steam-whistle, the shrill noise of 'the common whistle has been avoided by dividing the bell into three compartments tuned respectively to the first, third, and fifth of the common musical scale which harmonize and give an agreeable chord. Correspondingly, my multi le diaphragms could be named chime diap iragms.

The 20 millimeter iron diaphragm has a fundamental note of 1042 vibrations per second, and the 20 millimeter aluminium diaphragm of 2113 vibrations per second or about twice as many.

Hence, the double 20 iron diaphragm will have the same fundamental as the 20 aluminium, and indeed, the combinations double 20 iron+20 aluminium, and also 1% iron-{-20 aluminium, gave that disagreeable whistle, although somewhat less distinct than obtained by one diaphragm, whereas 20 iron+20 aluminium, or double 2O iron-l-double 20 aluminium, gave a false tone of less relative intensity and of better quality or timbre.

Other combinations were also tried out, but the best combination was obtainedby the combination of 4 diaphragms, 20 iron+20 aluminium-{44 aluminium+10 aluminium, forming a succession of octaves and combin ing together to form a tone of the tonal quality of an orchestral string instrument, compared with the cymbal tone produced by one diaphragm.

In Figure 10 is shown a combination of two iron diaphragms 12 and 13, of double and single thickness, for a radiophone receiver. Near their edges, they are separated from one another by means of a thin flat copper ring 14, and at their centers by means of a little piece of the same material and thickness 15, and these were soldered to both diaphragms. The box is only 1 millimeter thick and fits in a well-known brand of radiophone receiver, as shown in Figure 11, in which only the ebonite cap 0, and

the multiple diaphragm 12 and 13 are shown in sectional views: 1 l

The total volume of sound is, as might be expected, loss than that of the other headphone comprising one diaphragm, but. the false tone is relatively less distinct and of better timbre.

A good total volume of sound may be obtained by using relatively thinner (lia phragms. In general, it will be preferable to use homogeneous material for the diaphragms of diiferent thicknesses. Not only in the phonograph reproducer and in the telephone receiver, but also in the recorder, the transmitter, the loud speaker, and in other sound producing instruments in which a diaphragm vibrates, more or less complicated multiple diaphragms or chime diaphragms may be used with advantage.

While the construction, arrangement, and material of the multiple diaphragms, as herein described and claimed, are generally preferred, obviously modifications and changes can be made without departing from the spirit of the invention or the scope of the claims.

What I claim as new and desire to secure by Letters Patent is:

1. A multiple diaphragm comprising two spaced parallel diaphragms which are rigidly connected at their centers and firmly held in position at their edges and, com pared with one another, are of different thicknesses, the ratio of which can be expressed by small whole numbers.

2. A multiple diaphragm comprising two spaced parallel diaphragms which are rigidly connected at their centers and firmly held in position. at their edges and, compared with one another, have different areas of vibration, the ratio of which can be expressed by small whole numbers.

3. A multiple diaphragm comprising two spaced parallel diaphragms which are rigidy connected at their centers and firmly held in position at their edges and, compared with one another, are of different thicknesses and have different areas of vibration and of which the ratio of the two quotients thickness area can be expressed by small whole numbers.

4. A multiple diaphragu'i comprising two spaced parallel diaphragms which are rigidly connected at their centers and firmly held in position at their edges and, compared with one another, are of di'll'erent materials and of which the ratio of the two quotients QQEEIGSS {elasticity area {density can be expressed by small whole numbers.

5. The structure of claim 1, further char- 7. The structure of claim 4, further char- 10 ZlCtGllZQd by a ratio of the two thicknesses acterized by a, ratio of the two quotients about as 1:2. 7

6. The structure of claim 3, further clizir- 5 actel'izecl by a ratio of the two quotients w/ y i l i thmkness about us 1.2. W In testimony whereof I atlix my signature.

about as 1:2. MARI E. \VOLVEKAMP. 

